Device for introducing gas into a fluidised bed and method for therefor

ABSTRACT

The present invention relates to a device and a process for introducing gas into a fluidised bed reactor having at least one gas inlet pipe ( 2, 3 ) located underneath and/or above the fluidised bed for introducing gas into the fluidised bed, characterised in that the gas inlet pipe ( 2, 3 ) has gas-swirling means upstream of and/or at its mouth.

The invention relates to a device for introducing gas into a fluidisedbed, and to a fluidised bed reactor comprising such a gas introductiondevice. The invention relates also to a process for the oxychlorinationof ethylene to form 1,2-dichloroethane using a fluidised bed reactoraccording to the invention.

Fluidised bed reactors usually comprise a bed of a fine-grained solidwhich usually acts as catalyst for the reaction being carried out. Thesubstances that are reacted in the reactor are most frequently gases, asare the reaction products leaving the reactor at its head. Theintroduction and mixing of the reactants takes place in the lowerportion of the reactor, especially above and/or below the fluidised bed.An important role in the optimisation of the reaction is played by thegas inlet and distribution systems with which the reactants are mixedand brought into contact with the catalyst. The fluidised bed ismaintained in a suspended state by the gases introduced or by inertgases and thus has a fluid-like character. In the case of exothermicreactions this facilitates the transfer of the heat of reaction tocoolants which circulate, for example, in internal components especiallysuited to that purpose, such as pipes, in the reactor. On the otherhand, endothermic reactions can be assisted by special heating devices,for which purpose heating panels, for example, are used.

After the gaseous reactants have been passed through the fluidised bed,the gas current leaving the fluidised bed entrains fluidised bedparticles which, on economic and ecological grounds, have to beseparated out and returned to the fluidised bed. Suitable devices forretaining the fluidised bed particles are, for example, centrifugalseparators and filters. In most cases, however, it is not possible forall the fluidised bed particles to be separated, fine-grained particles(for example catalyst dust), especially, being lost. The loss ofcatalyst associated with the loss of fluidised bed particles thereforerepresents a considerable economic limitation. Furthermore, catalystsoften have toxic properties or are harmful to the environment, so thattheir separation and isolation from the reaction products can give riseto considerable expense.

It follows from the reasons given above that it is advantageous tosuppress the formation of fine-grained particles as comprehensively aspossible.

It is known that the formation of fine-grained particles is chiefly aresult of grinding and abrading processes within the fluidised bedagainst the cooling pipes and the reactor wall, or is caused by theintroduction of the gas. An increase in the formation of fine-grainedparticles can be counteracted, for example, by fluidised bed particleshaving a certain degree of resistance to abrasion. In the case of acatalyst applied to a carrier material, the resistance to abrasion isessentially determined by the carrier material. On the other hand,however, the use of abrasion-resistant (hard) fluidised bed particlesalso leads to increased wear on cooling pipes and the gas inlet pipesfor introducing gas into the reactor. As a result, high repair costs andrepair-related losses of production are likely.

The aim of the present invention is therefore to provide a device forthe improved introduction of gas into fluidised bed reactors in whichthe losses of catalyst caused by pulverisation of the catalyst anddischarge thereof with the gas currents can be reduced at the leastpossible expense.

That aim is achieved by a device for introducing gas into a fluidisedbed having at least one gas inlet pipe (2, 3) located underneath and/orabove the fluidised bed, which device is characterised in that the gasinlet pipe (2, 3) has gas-swirling means upstream of and/or at itsmouth.

Advantageous configurations of the invention are given in the subsidiaryclaims. The fluidised bed may be present especially in a fluidised bedreactor, preferably in a vertical fluidised bed reactor. The jacket ofthe reactor can be in the form of a pressure-bearing jacket forreceiving the gas or the gases and at least one fluidised bed ofparticulate solids located therein.

The gas introduction device according to the invention is characterisedin that the gas inlet pipe(s) effect(s) swirling of the transported gascurrent.

Surprisingly, it has been found that pulverisation of the catalyst canbe drastically reduced by a simple modification of the gas inlet pipesconventionally used, by means of which the gas current transported inthe gas inlet pipes is swirled. Such swirling of the gas currentpresumably has the result that the velocity profile of the gas currentbeing discharged from the gas inlet pipe changes in favour of a rise inthe volumetric flow in the vicinity of the pipe wall. For example, theswirled gas currents emerge from the gas inlet pipes with a velocityprofile that is approximately constant over the cross-section of the gasinlet pipe.

When the gas inlet pipes are arranged underneath the fluidised bed, theswirling of the gas current and the resulting modification of thevelocity profile of the volumetric flow largely or completely preventsfluidised bed particles at the margins of the gas inlet pipe(s) fromfalling into the pipe(s) and being pulverised therein to formfine-grained particles capable of being discharged from the reactor.Advantageously, therefore, a reduction in the dust discharge isachieved.

When the gas inlet pipes are arranged above the fluidised bed, it hasbeen found that in this case too the formation of dust and dustdischarge are reduced. In particular, a reduction in the wear on gaspipes and cooling pipes can also be achieved as a result. The reason forthis is presumably that during discharge of the gas current the gasbubbles are not immediately directed upwards.

In an advantageous embodiment of the invention, swirling of the gascurrent transported in the gas inlet pipes is effected by thegas-swirling means—especially at their outlet-side end—forming anarrowing or widening of the pipe lumen. Such a narrowing can take theform, for example, of a bead, for example an annular bead, arrangedaround at least part of the inner circumference of the gas inlet pipe.The narrowing or widening of the pipe lumen can take the form of athread arranged on the inner circumference. It has proved especiallyadvantageous for the narrowing to be provided with at least one edge,especially a sharp edge, because this favours swirling of the gascurrent. Furthermore or in addition the gas-swirling means can have atleast one screen and/or at least one turbulence grid and/or at least oneperforated diaphragm. The gas-swirling means can be arranged at themouth of the gas inlet pipe(s) and/or upstream of the mouth of the gasinlet pipe(s) in the direction of flow.

The invention will be described in greater detail below by reference tothe description of an embodiment, reference being made to theaccompanying drawings.

FIG. 1 shows a diagrammatic view of a fluidised bed reactor havingconventional gas inlet pipes for introducing gas currents into thefluidised bed;

FIG. 2 shows a diagrammatic view of a fluidised bed reactor having gasinlet pipes for introducing gas currents into the fluidised bed inaccordance with the present invention.

Referring firstly to FIG. 1, FIG. 1 shows a fluidised bed reactor havinga pressure-resistant casing 1, a fluidised bed 4 and, located therein, adevice for introducing gas into the reactor. The gas introduction devicecomprises a plurality of gas inlet pipes 3, which are arranged above thefluidised bed 4, for introducing gas currents into the fluidised bed 4from above and a plurality of gas inlet pipes 2, which are arrangedunderneath the fluidised bed 4, for introducing gas currents into thefluidised bed 4 from below. As shown in diagrammatic form in the twoenlarged views of the gas inlet pipes arranged above and underneath thefluidised bed 4, in the case of the gas inlet pipes customary in theprior art a substantially parabolic velocity profile of the gas currentbecomes established over the cross-sectional area of the pipe. Thereactor shown in FIG. 1 has a diameter of 28 cm and a height of 2.3 m.

Referring now to FIG. 2, FIG. 2 shows a fluidised bed reactor having gasinlet pipes for introducing gas currents in accordance with the presentinvention, which differs from the reactor shown in FIG. 1 in that thegas inlet pipes of the device for introducing gas currents of FIG. 2 areprovided, in accordance with the invention, with a narrowing of the pipelumen for swirling the gas current. The gas inlet pipes 2, 3 have forthat purpose an annular bead 6 which is arranged around the internalcircumference at their outlet-side end. As shown in diagrammatic form inthe two enlarged views of the gas inlet pipes arranged above andunderneath the fluidised bed 4, as a result of the annular bead 6 theparabolic velocity profile known for the pipes in the prior art isflattened off in favour of an increase in the gas current velocity inthe vicinity of the margin of the pipe. In particular, the velocityprofile of the gas current emerging from a gas inlet pipe issubstantially constant over the cross-section of the gas inlet pipe.

The fluidised bed reactor of FIG. 2 is especially suitable for theoxychlorination of ethene, which will now be described by way ofexample.

Oxychlorination is understood generally as meaning the reaction of analkene—in this case ethene—with hydrogen chloride and oxygen or anoxygen-containing gas, such as air, to form a saturated chlorinatedalkane—in this case 1,2-dichloroethane, referred to as “EDC” below—inaccordance with the equation:C₂H₄+2HCl+½O₂→Cl−CH₂−CH₂−Cl+H₂O

For this reaction there is used, for example, a catalyst in the form ofcopper(II) chloride applied to aluminium oxide particles. The catalystparticles have, for example, an average particle diameter of about 50μm, with a particle range of from 20 to 120 μm. The particle density isapproximately 1600 kg/m³ The inflow of circulating gas and reaction gascause the catalyst particles to form a fluidised bed.

In the fluidised bed reactor according to the invention of FIG. 2, thereactants, which are heated to 150° C., are introduced in gaseous form,a mixture of 63 Nm³/h of hydrogen chloride and 17 Nm³/h of oxygenflowing into the catalyst fluidised bed 4 through the gas inlet pipes 3arranged above the fluidised bed 4. A mixture of 32 Nm³/h of ethene and60 Nm³/h of circulating gas flows into the catalyst fluidised bed 4 frombelow through the gas inlet pipes 2 at a temperature of 150° C. and apressure of 4.7 bar. The average flow velocity is 1.3 m/s in the gasinlet pipes 2 and 1.0 m/s in the gas inlet pipes 3.

In the lower portion of the fluidised bed 4, the reactants, which aredistributed over the reactor cross-section, are mixed in the so-calledmixing zone and react exothermically on the catalyst. The heat ofreaction of 238.5 KJ/mol thereby produced is conveyed by way of coolingpipes (not shown) to a heat transfer medium. The reaction temperature is232° C., at a reaction pressure 4.2 bar.

Measurements of the amount of fluidised bed particles before and afterthe reaction have shown that the loss of catalyst caused bypulverisation and by discharge of catalyst particles by way of theoutflowing gas is approximately 7.6 g per t of EDC.

COMPARISON EXAMPLE

For comparison, the oxychlorination of ethene to EDC is carried out inthe conventional fluidised bed reactor of FIG. 1, the conditionsotherwise being the same. Measurements of the amount of fluidised bedparticles have shown that the loss of catalyst per t of EDC isapproximately 48 g, that is to say about 7 times the amount of the lossin the case of a fluidised bed reactor according to the presentinvention.

1-14. (canceled)
 15. A device for introducing gas into a fluidized bedcomprising: at least one gas inlet pipe located underneath and/or abovethe fluidized bed, wherein the gas inlet pipe has gas-swirling means atits mouth.
 16. A device of claim 15 wherein the gas-swirling means format least one narrowing or widening of the pipe lumen.
 17. A device ofclaim 16 wherein the narrowing has at least one edge.
 18. A device ofclaim 15 wherein the gas-swirling means comprise a thread.
 19. A deviceof claim 15 wherein the gas-swirling means comprise at least one bead.20. A device of claim 15 wherein the gas-swirling means comprise atleast one screen, at least one turbulene grid and/or at least oneperforated diaphragm.
 21. A device of claim 15 wherein the gas comprisesethane, oxygen and/or hydrogen chloride.
 22. A fluidized reactor bedcomprising a device of claim
 15. 23. A process for the production of1,2-dichloroethane with a fluidized bed reactor comprising a device forintroducing gas, the method comprising: introducing ethane, oxygenand/or hydrogen chloride into a fluidized bed comprising a catalyst,wherein the device comprises at least one gas inlet pipe locatedunderneath and/or above the fluidized bed and the gas inlet pipe hasgas-swirling means at its mouth.
 24. The process of claim 23 wherein thegas inlet pipe is arranged underneath the fluidized bed and the gascurrent is discharged at an average discharge velocity in the range offrom 0.5 to 10 m/s.
 25. The process of claim 23 wherein the gas inletpipe is arranged underneath the fluidized bed and the gas current isdischarged at an average discharge velocity in the range of from 3 to 6m/s.
 26. The process of claim 23 wherein the gas inlet pipe is arrangedabove the fluidized bed and the gas current is discharged at an averagedischarge velocity in the range of from 0.7 to 10 m/s.
 27. The processof claim 23 wherein the gas inlet pipe is arranged above the fluidizedbed and the gas current is discharged at an average discharge velocityin the range of from 2 to 5 m/s.